Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $33.98   10.635%   $37.5938   $37.59   $37.60   $37.60  
  Purchase #2 $180.97   11.793%   $202.3118   $202.31   $202.30   $202.30  
  Purchase #3 $16.59   4.418%   $17.3229   $17.32   $17.30   $17.30  
  Purchase #4 $95.49   12.617%   $107.538   $107.54   $107.55   $107.50  
  Purchase #5 $99.72   12.156%   $111.842   $111.84   $111.85   $111.80  
  Purchase #6 $32.88   13.146%   $37.2024   $37.20   $37.20   $37.20  
  Purchase #7 $239.67   8.527%   $260.1067   $260.11   $260.10   $260.10  
  7 purchase totals = $699.30       $773.9176   $773.91   $773.90   $773.80